1. Field of the Invention
The present invention relates to a variable compression ratio apparatus. More particularly, the present invention relates to a variable compression ratio apparatus which changes a volume of a combustion chamber such that a compression ratio is varied.
2. Description of Related Art
Generally, thermal efficiency of a heat engine is increased when a compression ratio is higher. Here, the compression ratio is a ratio of a volume of a gas which flows into a cylinder and is compressed by a piston, and is represented by “cylinder volume/combustion chamber volume at top dead center of a piston”. That is, as the top dead center of the piston becomes higher, the compression ratio is increased.
In a case of a spark ignition engine, thermal efficiency may be increased by advancing ignition timing, but there may be a limitation in the advance of the ignition timing considering abnormal combustion and the like. Accordingly, a variable compression ratio (VCR) apparatus for improving thermal efficiency of the heat engine is demanded.
The variable compression ratio apparatus is an apparatus for changing a compression ratio of mixed gas according to an operational state of the engine. The variable compression ratio apparatus functions to improve fuel efficiency by improving a compression ratio of mixed gas under a low load condition of the engine, and prevent generation of knocking and improve output of an engine by decreasing the compression ratio of the mixed gas under a high load condition of the engine.
An ordinary variable compression ratio apparatus uses types that move a cylinder block, change a volume of a combustion chamber, and change a top dead center point of a piston.
However, many mechanical constituent elements are required and the composition thereof is too complex for realizing the ordinary variable compression ratio apparatus. In addition, fuel consumption may be deteriorated in a case that a motor using electric power is used so as to operate the mechanical constituent elements. Furthermore, a relatively strong driving torque is required for transferring power of a motor compared to other gear coupling. Therefore, it is limited that the capacity of the motor is reduced. Meanwhile, it is not easy to realize quick responsiveness of a variable compression ratio apparatus if the mechanical constituent elements are complexly connected.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.